The Bahia Seamounts: test of a hotspot model and a preliminary South American Late Cretaceous to Tertiary Apparent Polar Wander Path

Abstract

Detailed bathymetric and magnetic data collected over the Bahia Seamounts in the western South Atlantic (Brazil Basin) are analyzed. Six paleomagnetic poles are determined, one from three seamounts sharing a ridge, and five from isolated seamounts. Two poles fall near a continental Late Cretaceous South American pole and are assumed to be of Late Cretaceous age. Another seamount has a preliminary 40 Ar 39 Ar age of 62 ± 4 Ma. We check this age and estimate the ages of other seamounts by rotating their poles into North American coordinates and comparing them with North American paleomagnetic reference poles. These ages and the characteristic magnetic polarities of all Bahia Seamounts are used to test hotspot models of formation of the seamount group. The northern and central Bahia Seamount chains could have formed from a single hotspot. The southern Bahia chain may require a second hotspot. The two postulated hotspots were probably concurrent and separated by 150 to 200 km. The paleomagnetic poles trace out a smooth curve from the Late Cretaceous poles to a pole that is indistinguishable from the spin axis, which we estimate as having an Early Eocene age. The pole ages remain preliminary until better age dates are found and rocks are recovered from more seamounts.